A database is an organized collection of data, in digital form. The data in a database can be organized to model relevant aspects of reality, in a way that supports processes that require this information. A database can have a model that describes a theoretical foundation of the database and fundamentally determines in which manner data can be stored, organized, and manipulated in a database system.
A hierarchical database model is a database with a data model in which the data is organized into a tree-like structure. The structure allows representing information using parent/child relationships in which each parent can have many children and each child has one parent (also known as a 1-to-many relationship).